There have since been hundreds of demonstrations against Sterling's and Castile's deaths in U.S. cities -- while most have been peaceful, at least 309 people have been arrested in clashes between police and protesters.

How do they compare with the atmosphere in Europe?

London

Almost 1,000 people took part in rallies in the UK capital over the weekend, many saying they were there to show their support to black families in the United States.

Demonstrators make their way Sunday through London to show their solidarity with the U.S. protests.

"Every day I wake up another black person is dead -- that's why I'm here today," one protester told CNN.

One man was charged with being drunk and disorderly at a rally in Brixton, south London.

Berlin

Some protesters in Berlin were moved to tears Sunday during an emotional reading of the names of black people killed by police in the United States this year.

Protesters attend a Black Lives Matter rally Sunday in Berlin.

"When they read their names out loud, the whole crowd repeated it and said, 'Say their names' -- the list was so long though that eventually so many people started crying out in disbelief and horror," said protester Chelsea von Holst.

"It felt like even though I didn't know anyone, we were a strong group of friends who all wanted to protect each other. It was quite remarkable."